Electrical pilotage



Dec. 25T, 1928. 1,696,230

J. J. GILBERT Y l ELTRICAL PILomGE Filed June $0-, 1925'- 2 sheetssheet 1 @fag/WW@ I i l -cable can be determined.

"teamed "Dee 2 5, 1928, j

s JOHN J. GILBERT, or rom: wn'snnmron, NEW roux, nssmnon 'ro was'rnm zum l TRIO COMPANY, INCORPORATED, OIF NEWYOBK, N.. YQ A CORPORATION v0l' NEW application mea June'so,

- For thev purpose of guiding ships through Cable induces electromotive forces in. coils which are located on ship board, and by com-A paring the electromotive forces in the various coils the position of the ship relative to the An object of the present invention is to increase the magnitude of this field. is done, first, by improving the transmlssion characteristics of the cable,` which *determine* 'the magnitudeof the current inthe cable at an e da to a multiple of the half wave length o current therein orby loading the cable or` by both of these means; and second, b modifying the structure of the sheath o armor wires, which determine the distribution of the return current inthe Water vand the value of the magnetic field at a' given distance from ,the cable. l

Referring to the drawings, Fig. 1 illustrates diagrammatically a cable and source of'alternating current arranged, according to the present invention, for guiding the ship, which is provided with'suitable receiving apparal tus. Fig. 2 is a detailed view of a submarine cable which is loaded and armored in accordance with the present invention. The curves in Figs`.3, 4 and '5 have been labeled to indicate what they represent. They will -be referred to in detail later on.

Referring. in detail wrig. 1 of the draw! ings, a submarinecable 1 4loaded and armored' as hereinafter explained, is connected at onev end to the ground 2 and is in circuit with a source of alternating current 3, the frequency'V It isevident that Is reaches its maximum value when s=mr and as=0, that is, when the length of cable is a multiple of one-half Wave length and the total attenuation is zero.

quired to obtain the maximum effect depend-l Ollt, by making the length 0f the Cable' ing upnthe length lof the vcablean'd 4upon 1923. serial ne.' rinasce.v

of which is chosen as hereinafter explained. The generator 3 is grounded at 4,4 as usual,

` to provide areturn path for the currents through the water. The ship 5'is provided i wlth the vusual coils 6 and 7, -which are connected by meansof the reversing switch 8 to any suitable 'detecting and amplifying apparatus A, which supplies the detected and amplified currents to the receivers l0. ,Consideration will now givento' the detics of the cable and to the structureA of the armor. Other things being kept constant, the electromotiveforce observed on shipboard lis directly proportional tothe currentin` theadf This current Vcan j ,ioacent section of the cable'.

e increased by a suitable degree of inductive loading, whic may be calculated as herein-v after explained, the amount of loading ref` where Z=the characteristic impedance 5f-'15 the cable, y=alj=the propagation constant of the cable, Vo=the input voltage. j

The components of the propagation constant are calculated from'the formulae:

ance, inductance, leakance vandcapacitanc'e per unit length. Y Equation (1) gives for the current at the distant end the value g l nanou athis lima ef zero attenuation is unt5 attaina le in practlce, we may approach itby. suciently increasing the. inductance of .the

cable to reduce the attenuaton ,and at the s terminationof the transmisslon'- characterisf R, L,'G*and C being rf'aspectivelythe'resistsame time maintain the wave length" rela. tionship without undul increasing the impedance of the cable. specific example of -how these variables are chosenyis given later on.

io is ofthe ordinary non-loadedtype. The other is identical in structure, exc'e. t that some of s n .l

l I lf .y v where ii is the permeability of the loading mathe` copper of the core con uctor 'has .been replaced by a layer of high permeability material, thus increasing the inductance .715) unit len th ofthe cable..v As developed mat ematical y above, standing waves are produced \on a cable whose distant end is grounded or 2o taneous valuesof the current at the time of..

maximum 'amplitude and over a complete c otherwise terminated so as to. produce reflection effects. The diagram shows instan# cle the current will decrease to zero, rise to t e maximum value 1n the opposite.' direction and again assume the value shown. But these '4525 periodic chan eswill only 'occur at fixed points spaced the cable and at the intermediate nodal p oints y practically no current will ever flow. ereafter in the specification the points of maximum` and'A minimum current flow will be referred to as current loops and nodes, respectively. Comparison ofp-the curves in Fig. 3 indicates two points of superiority of the loaded cable first, the larger value of current amplitude at points onA the cable remote fromthe generator, and second, the'shorter length of the silent zone, indicated by the dotted lines inthe figure, in which the current amplitude is-less than the value required to give recognizable effects onv shi board.

- The number and location of t e current loops along the cable may be controlled by the degreeof loading and' by the choice of frequency. Thus, `if at particular points in the channel,v it is' desired to obtain a maximum effect in'the detecting apparatus the cable can be designed. to give current loops at those points. vThe increased current amplitude that results from loading-Will be found` of great advantagewherelong'cables (more than 100 nautical miles) are to be employed, for the purpose, say,of outlining a strip of f ,The following appl-iles in the choice of a v r ,s'

loading inductance to be employed in any particular case. The fundamental equation is r s.=mr (2). lwhere ,B is delinedby the equation- #pif-Lo 3) e which. is a very-close approximation for the the formula given above. The loading inducyhalf a wave length alongI This inductance4 canV be'obtained by a numl ber of choices of thickness andlpermeability of loading'material, asis indicated by the formula L: 77.42.1210 itp.@

terial, tis the thicknessof this layer and d' is its' mean diameter on therconducton L is the inducta-nce vin henries per nautical mile.

of the conductor and therefore increase the A attenuation, a ,certain set of values of p and t will be found to be most suitable for obtaining a given value of L,'aiid'thesefwill be designated as the optimum values of these t uantities. The eddy current resistance is etermined'by the formula Rfk/Lf@ j (6) i' i where lc is a constant de endin upon electrical characteristics of t e loa ing material and its geometric form.`v

l The quantitynl is the number of half wavelengths contained in the entire length of cable. The choice of this quantit may be regulated to-a certain extent by t e nature of the course of the cable. Thus if it is particularly desirable/to mark out certain parts of the course to a greater degree than other parts, it will be desirable to select n so that the loops of current will be located at the desired points. In this same connection it may be found desirable in certain cases to impress ioo simultaneously on the cable two or more diftonev at any point of the cable might be used as an additional means of marking.

By taking various values of n we arrive at a number of values of loading inductance according to formula (2), which will give the desired wave-length characteristic. The attenuation constants of these various values of L will diii'er among themselves' owin to the fact that various optimum permea ilities and thicknesses of loading material have been employed. This will serve as another factor influencing the choice of loading inf ductance; since other things being equal, 4the valueof L corresponding to the smallest attenuation constant would be the most desirable one to employ.

Yl`here is still a third yfactor of influence upon our choice, namely, the fact that the inductance of the cable iniuencesthe characteristic impedance of the cable, as indicated by the formula f ZV1/o (7) r It is found that the optimum values of permeability described abovearehigher than those that can be obtained by the use of ordinary material such as iron. They can, however, be easily obtained by the use 0f an iron nickel alloy, which .as described and claimed in G. W. Elmen application, Serial No. 557,928, May 2, 1922, is composed preferably of 7 81/2d per cent nickel and 211/2 per cent iron though .other proportions may be used. The permeability of this alloy at small magnetizing forces of the order of0.001 to 0.10 gauss has been found to be from tento twenty times that of iron, that is, from 1000 to 6000. Any other suitable loading may be used however.

ln Fig. 2 of the drawings the stranded electrical conductor 11, which may be of copper and from 100 to -200 mils in diameter, is illustrated as having aspiral wrapping 12 of iron nickelalloy,.which maybe 3 to 10 mils thick and from 20l to 200 mils wide, al-

though other dimensions may be used, and which may comprise one or more layers. It is pointed out in the above noted -application that iron nickel tape is wrapped while cold on an electrical conductor, and is later treated by heating the taped conductorto a temperature of about 850 C., maintaining it at that temperature for a few minutes to insure a uniform temperature throughout, then cooling slowly to a temperature of about 600, which is )ust above the critical or transition temperature of the alloy, that is, the temperature at which the magnetic properties disappear on heating and reappearv on cooling;v and inallycooling vfrom that temperaature more rapidly but at adefinite rate dependent upon. the ratio:of'fnickel tqiron in the alloy. This rate can be easil determined by trials. A convenient metho` of securing the 'desired rate .of cooling has been found to 'be' arapid withdrawing of the material from the furnace when it has reached the.`

temperature of 850 C. into a blast of air or inert gas which is controlled to secure the v desiredyrate of cooling. The necessary cooling will always be at a rate intermediate that .require-d for annealing and that at which such internal strains would be set up as to '-loylver the permeability below the desired va ue.

treated, as indicated above, it is provided with a coating 13 of gutta percha or the like and` a coating 14 of jute r the like, on top of After the taped conductor has, been yheat- I which'isflaid the armor 15 comprising wires or bars, which are spaced apart for reasons described in detail below. On top of the armor 15-one or more coatings 16 of jute or Athe like may be used.

`Regarding the second controlling factor,

the'effect of the structure of the sheath upon the current distribution in thev sea water, a

r study of the general problem of Vsubmarine cable ,transmission shows that at audio requencies'the return current in the sea water and armor wires is concentrated, to a large' degree, in the neighborhood of the core, and

that the degreel of concentration depends .upon the frequenc ,and upon the structure and the material o the armor wires. This is shown in the curves of Fig. 4 which gives the l percentageof current carried by the armo-r wires for a submarine cable in which two arrangements o armor wires are employed. In the closed .arrangement the armor wires are laid on the j utein sucli a manner that ad- `jacent wires are in contact. In the open ar rangement there is an interval, amounting -to a fraction of the vdiameter of an armor wire, f

between'adj acentwires.

The vmagnetic eld intensity in the water at vany distance lated by rigorous analytical methods and is expressible in the form I. g

- where r and pn are, respectively, the distances of the 'point from the cable core and from a particular armor wire designated as the nth;

@n is the relative orientation of the point and Bessel function of the second kind and ofthe Sth order;..-A and B, are constants, and a is defined by the relation,

in Whichj 1/ 3 1' and f is the frequency The magnetic ield intensity at a point feet from the cable :forv both the open and closed arrangement of armor wires previously described are given in the curves of Fig. 5 as from the cable can be calcufunction of thev frequency. It is'obvious that l the open arrangement of armor'wires is ,su-

perior for the purpose which We are discussvfield intensities. ment for the purposes of electrical 'pilotin'- ing, in thatit permits the return current to penetrate the armor sheath andto escape into the surrounding*Water; y

Still greater improvement inthis respect can be obtained'- by Wires entirely' and obtaining theV required mechanical protection by a 'heavy layer of J The current in the sea- Water is then able to spread through a much largercross section' with resultant increase in the value of the" electric and magnetic iieldsatall points. For the same reason, the resistance 4of thev cable circuit is much less ,in this case, and the lcurrent at all points'in the cable lWillthere-V further increasing the fore be increased, thus Therefore,

preferably consists of a central insulate core, loaded continuously with high' `permeability material, surrounded by a layer of jute or other non-magnetic and poorly conducting material` to chanical protection. v v

What is claimed is:

1; A magnetically loaded submarine piloting cable having one end terminated in an impedance of value relative to the charac- A tcristic impedance of the cable such that dispensing with armor give the required me-4 electric waves are -reiiected' therefrom, and

`means for supplying valternating current to' the other end of the cable, the length of said cable being ,a multiple ofone half wave length f of the electrical waves supplied by said means.

2. The method of* obtaining a maximum.

external magnetic field at a particular -longitudinal point on a pilot cable which comprises so terminating the cable as to produce reiected electric Waves, applying an exciting E. M. F. to a circuit including the pilot cable and so regulating the frequency of the exciting current with respect to the inductance'y and-length of the cable as to produce a current loop at said longitudinal point.

. A ically loaded submarine piloting cable havin one end connected 'directly to-V ground, and means for a plyin alternating current to the other end oi) the c5) half thewaye length of the electrlcal wave supplied by said means. v 4. A. piloting circuit comprising an electrical conductor continuously loaded with magnetic material throughout atleast that portion of its length Where it is desired' to produce an external electromagnetic iield.,-

In witness whereof, I hereunto subscribe my name this 27th day of June A. D., 1923.

JOHN JGILBERT.

le ofsuch frequency that v the length of said cable is am'ultiple of one.v

piloting circuit comprising a ma'gnet-v Ili() 

